This invention relates to a control apparatus for a direct injection type internal combustion engine.
An accumulator type fuel injection control apparatus is well known as an apparatus for feeding fuel into the plural cylinders of a direct injection type internal combustion engine. According to this type of fuel injection control apparatus, fuel is pressurized in the fuel rail (common rail) by the use of a fuel pump and then is injected into the cylinders through the injectors mounted on the fuel rail. Further, this fuel injection control apparatus makes it possible to obtain such an optimal fuel injection quantity as to stabilize fuel combustion by making the pressure of fuel in the rail variable.
With the accumulator type fuel injection control apparatus as described above, the pressure of the fuel in the fuel rail (hereafter also referred to simply as “fuel pressure”) pulsates due to the feed (hereafter referred to also as “discharge”) of fuel from the fuel pump to the fuel rail and the injection of fuel through the injectors. This change in the fuel pressure directly affects the amount of injected fuel. Consequently, precision in the control of the air-fuel ratio deteriorates with the result that the exhaust emission is adversely affected.
A method wherein a desired fuel injection quantity can be secured by measuring the fuel pressure in the fuel rail and controlling the injection of fuel in accordance with the measured pressure, is disclosed in, for example, Japanese patent documents JP-A-2004-346852 and JP-A-2006-57514.